Re: [PATCH v6 06/23] sched/fair: Load balance only among preferred CPUs

[Yury Norov <yury.norov@gmail.com>]

On Wed, Jul 01, 2026 at 07:46:37PM +0530, Shrikanth Hegde wrote:
> Consider only preferred CPUs for load balance.
> 
> With this, load balance will end up choosing a preferred CPUs for pull.
> This makes it not fight against the push task mechanism which happens
> at tick. Also, this stops active balance to happen on non-preferred CPU
> pulling the load.
> 
> This means there is no load balancing if the task is pinned only to
> non-preferred CPUs. They will continue to run where they were previously
> running before the CPUs was marked as non-preferred.
> 
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>  kernel/sched/fair.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ce05acf52d35..9b2931b559d6 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -13391,7 +13391,8 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
>  	};
>  	bool need_unlock = false;
>  
> -	cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask);
> +	/* Spread load among preferred CPUs */

We don't have a "Spread load among active CPUs" comment. Don't think
it's more difficult to understand what happens if you replace one mask
with another.

> +	cpumask_and(cpus, sched_domain_span(sd), cpu_preferred_mask);
>  
>  	schedstat_inc(sd->lb_count[idle]);
>  
> -- 
> 2.47.3